Signaling by high-frequency waves



May 12, 1925.

F. W. KRANZ SIGNALING BY HIGH FREQUENCY WAVES Filed spt. 29. 191g l mi we inail Application .flied September oi variations in a high frequency wave such'v :is occurs in high frequency,telephony ln such a system a high frequency Wave is controlled for transmission oy wares of comparativel7 low Yfrequency and the com,- plex Wave so produced is applied at the reycer-.fer to a freqwhey-modifying device cord monly called a detector or demodulator, the purpose of which is to produce as a separate component the low frequency Waves Which it is desired to receive. It is Well known that a great .number of combinations of frequencies may he produced by the detector, onlg7 some of which are desirable or necesn sary for signal recepion. llfhe presence oi? frequencies other than those comprising lhe signal ware servos to confuse the signal and impair rho qnalily` This especially lrne in high irezjucnq' telcphony'since the voice wave a highly complex wave which must he reproduced to a nicely in order to ohtain good quality of voicetransmission. The interaction;between Jthe various 'frein the process oi deflection produces 29, i919. Serial Elo. 327,95).

ferent frequencies is proportional to the product of the twowaves end from this it follows that the Wave of carrier frequency should loe large compared with the received frequencies representing she signal modulated componeng which are to interact in the detector to produce the desired signal frequencies. If this. ratio is suciently large, the disturbing components, dueto interaction between portions of the sional Wave itself, Will be scarcely or not atall noticeable in their effect upon the quality.

For controlling the high frequency Wave by the signaling Wave or other low frequency Wave to he transmitted, a modulator is used. ln general the modulator may perform several functions at the same time, vl'among which are modulation and amplifica- `tion. if the modulator is adjusted, to have maximum eliiciency for one of these two functions, the other function is greatly diminished. Thus to modulate at its highest ehciency the modulator would not amplify the separately impressed Waves to any great extent and the resultant Wave would be a modulated Wave having a small ratio oi carrier Wave to modulation component, this ratio is to he large a sacrifice must he madein the eliciency of modulation. Heretotorc the 'modulator has heen adjusted togivc n comparatively large ratio of carrier wave to modulated component at the expense oi? the modulating efficiency.

The present invention com )rises method and means l'or improvingl the lpuality of the received speech or other signal hay obtaininjbr a su'liciently large ratio of carrIer wave to ihe signal nurdulated component.

The invention further comprises method and means for providing an optimum ratio of carrier wave to the signal modulated component.

A feature of the invention is the separate supplyingI of the wave of carrier frequency to the system independent] yY of the modulator. This enables the modulator to be operated at it-smaximum etliciency'and still scriprion together with the accompaflying,`

l0( permits any desired ratio of carrier Wave to drawing'in which Fig. 1 represents a diagrammatic circuit arrangement ot' a system according tothe invention; Fig. 2 shows a curve representing measurements talren with apparatus according to the present inveu- -tion and made use of in the system accord in@ to the present invention.

-n Fig. 1 the heavy lines indicate one form of :s high frequency telephone system to which the invention is applicable, and the li ht linesindicate accessory apparatus W ich may he used for measuring or testing purposes, 'as' will he described hereinafter. The high frequency telephone line 1 is shoWnprovidedfWith apparatus for transslitting in one direction only, although hy arrangements known to those skilled in the art, it may equally Well serve for transmis sion in both directions and for simultaneous transmission of a plurality of high frequency Waves each of which may be separately controlled by signals. One such source ci? high frequency Waves' is shown as 4'an oscillator() of a Well-lnowu thennionic type, the frequency of which' he controlled hy the variable condenser C. For

"controlling the high frequency Wave produced h the source 0, a. modulator M is provide When the switch 5 is thrown in the upper position and switch 6 is closed, voice currents are produced in the circuit including'- the transmitter T5 cattery 9, .switches 5 and 6 and the '.,primary of the lcoupling 10, dueto speech Waves being directed against the microphone.` Bymea-ns of l the coupling 10 the speech waves. are, there" fore, 'impressed on the input circuit of the modulator M. The high frequency Wave from the source is supplied to the same input circuit through the amplifier A. which may he oi any suitable type, and is shown having its input circuit including an adjustable portion o the resistance included between the terminals l1 and 12 in the outputcircuit of the' oscillator O. The wave which is ampliied at A is applied through the circuit 13 to the potentiometer resistance 11i which isshown included in the input circuit of the modulator. As a result of the action of the modulator upon the two waves thus impressed upon it, a. voicen .modulated lhigh frequency Wave is transmitted through the coupling- 15 and through the filter F1 and the output coil 1S. With the type of modulator shown, the output currents will ordinarily contain as components, a wave-of the original carrier frequency' and two side bands of frequencies respectivelyhigher and lower than the carrier frequency and each having a frequency y range equal to-tliat of the voice currents ap-V pliedto the coils 10. The filter F1 is pret crahly so designed as to transmit onl one of these side hands or one of the side ands and the carrier frequency, since both side is operated .at its maximum eiiiciency forA modulation. These frequencies are transmitted from the coil 16 to the` conjugate, coils l which are provided in the branch 2 leadiircr to the line 1. vFor cooperating with the conjugate coils 4. a network 3 is indicated for a purpose to he described later on. A shielded transformer is indicated for coilpling :i brauch 2 to the line l.

ln addition to the n'xodulator and the coil 16. another circuit is provided according;r to the invention 'For transmitting a wave to the line. This circuit 17 leads directly from the terminals oi' the potentiometer resistance 11, 12 in the output circuit ot' the oscillator to the potentiometer 18. which has a sliding contact 19 for enabling a portion of the resistance to be bridged across thc midpoint of the coils 4. This arrangement permits a a wave of the carrier frequency from the oscillator to he impressed directly on the branch 2 independently of the oscillator Wave which is supplied to the modulator and permits the amplitude of the Wave so applied to he regulated. By means of the conjugate connection none. of theoutput current from the coil 16 finds its Way into the circuit 17 and thereby through the aux` plier to the input side of the modulator. Such a circulation of current under certain couditions'vvould produce singing.

For signal transmission it is assumed that the switches 7 and 8 are both closed.' The 1 Wave from the modulator and the Wave sepa. rately impressed on the line from the esci/lf lator. therefore, traverse the line land are `applied to the detector D. .An artificial line 20 is indicated which would ordinarily not' he used in a transmission systemhut which as here used simulates the characteristics of a line of any desired length inorder to' enable measuring or testing to be accomlill) plished as will be described hereinafter.

The Waves applied at detector D produce hy interaction a series of Waves, one of which represents the signal component to be received. The output circuit of the detector l) is shown as including a low-pass filter F2 and a receiver R. The filter F2 prevents the transmission to the receiver R of all frequencies higher than those comprised in the essential voice range.

It the proper ratio of carrier Wave to 'modulated component was lapplied at the trunsmittinfr station the disturbin curaf .i

rents produced by interaction of the frequencies comprising the voice wave "il he practically negligible in their effect Wave which is received at R.

An'f advantage of supplying the wave to the line at the transmitting mation @senses instead of at the receivinfr station is that the line loss is substantially the seme for the csr- ,rer component end the .modulated component, and therefore, the proper ratio ot carrier were to modulated comnonentfii once determined, will hold for various lengths of lines. This enables standardization of the 'apparatus to ai greater degree then if a sepa.-

rate carrier wave oscillator were supplied ef "fa ,01' the receiver. Another advantage is that sin le oscillator serves both to supply the .modu ator and to transmit come unnmduu lated carrier Wave component.

The accessory circuits hy which, according to the present invention, the proper retio ot' carrier to modulated components can he de- `tel-mined, wlll non7 he described. with the switch 5 still in the upper position and the switch 6 open. the voice currents in the circuit of the 'transmitter T are impressed through the thermocouple 28, and their inagnitude is indicated by the galvanome'ter 2"?. v'If now the switch 8 is open and the switch 21 is closed on the ri ght, the voice-modulated currentv transmitted over the line l. is receiyed through the receiver shunt 29. by the second receiver 23. For the description of a receiver shunt of the type indicated at 22,

reference muy he hsd to the patent to lllaclc well, 1,261,096, issued April 2, 19l8. A separate line is shown leading directly 'from 'the circuit of microphone T to terminals of the switch 2l and including the artificial line 24. lIf speech waves are continually directed against the microphone T and if the switch 21 is alternately thrown tothe right and to detector D from the high frequency wave4 i'vhlcll iynsorlgnmlly controlled hy voiceY "currents produced hv the' microphone T. By

fmeans of thcnrtilicial lines 20 and Qi the;

nmade the; saine.

loudness of the speech transmitted over the `.two pathsyand received in receiver 23 may be lf now the potentiometer 1S, 19 .is adjusted to impress n smalhamount .ot the carrier Wave com )onent on the line` it will he Yassumed that the unlity of the speech received through thel ugh frequency line is relatively poor. 'llie receiver shunt is now adjusted to attenuate the 'voice currents so received to the point where theyare just unintelligible. Also by varying the receii'er shunt 22, the Aamount of attenuation necessary to reduce a speech wave directly trensmitted from the microphone T to the receiver Q3 to the point of unintelligihility, cnnl be determined. This setting may be mede.

once for all, for a series of measurements and is indicated in n diagram of Fig--2 hy the horizontal line VW. For s giron sett intr of the potentiometer le, 19 a reading is made of the strength ot' the voice currents hy means oit the galvanomcter 27. The switch 5 is then thrown to the lower position to in clude the source 26 oit' sinenfavcs in the circuit leading to the modulator M, and the resistance shown in the circuit of generator 2G is adjusted lto give the same reading on the galvanometer as Wes obtained when speech waves were traversing this circuit. lt should he stated that the switch 7 is open in these tests and therefore the tuned circuit including variable condenser 29 and coil 3() use included in the one side of the 4lint` l. oil 30 is coupled to the coil 3l in the input circuit 1 'of the modulating Wave are respectively the same es those oi the carrier Wave and the rtuic'lulating0 wave when speech currents nere being transmitted. The purpose of suhstltuting the sine wave generator 26 in 'place of the source of speech currents is to give a delinite side 'frequency in place of a hand of side frequencies, in order that the side frequency may he completely seperated from the carrier frequency for purpose of measurement. The. tuned circuits 2i), 30 and 3l, 32 are ndjusted to selectively transmit the Wave ot' carrier frequency only and a reading is made. onv the galvanoxneter 35. The tuned circuits are thcn ad j usted to selectively tl'ansniitfonly the side frequency resulting from -the modu lation of the carrier were hy the wave 'from source 2G. trending is egsin runde on the galvanonieter 35. The frequency of the gen erator 26 is preferably at the mean 'speech frequency, say 1,000, and therefore, the filter F1, 1f adjusted to ,pass only one sideband of speech frequency, will sho pass only one of the side frequencies present when generator 26 is being used. The ratio of the two reed ings thus obtained on the galvanometer 35 is an indication oi' the ratio oi the 'carrier 'Wave component impressed on the. line to the modulated component in'ipresse'd on .the line l. This ratio .is indicated inllg. 2 es Since ,the magnitude of the Wave from source 26 was adjusted to oe equivalent to the voice currents from transmitter T, the

ratio also n'idicstes therstio ot the carrier C wave, the ratio S thus obtained, indicates the ratio ot' carrier wave to uunlulated component impressed ou the detector l). To obtain the curve N.ot` Fig. i2, the ratio plotted against'the amount of attenuation necessary in the rcccii er .shunt to reduce the speech receivedover the high frequency channel to the point ot' unintelligihility. To obtain another point'ou the curve thc potentiometer 1S, 15) is adjusted to supply a larger amount ot' carrier wave component to thc line. thcY artilicial lines '.11 and Qt are again adjusted if necessary to give the same Aloudness o1 the .signal received at 23 over the high frequency line as over the low frequency line when the receiver shunt22 so adjusted as to give good quality to the sifeech transmitted over each path` the amount of attenuation necessar)v at Z2 to reduce the in- Atelligribility of the signal received throngn the high frequency channel to zero is aga'a'n noted and a comparison 1s made andr reacts;- ings are taken as before to obtain the ratioV By proceedngin this manner, al number S of points ma)v be found which will determine a curve such as indicated b v N. Since the basis of comparison is the reproduction of voice currents b v a simple receiver 23 as compared with reproduction of the same currents b y the hi'ofh frequency apparatus` it is' evident that tie curve N will never rise above the horizontal line VNV. On .the other hand. it'may be shown that the curve is asymptotic to the line VV since the disturbing currents'introduced'by the detector D which, are entirely absent in thecase of the seen that for a ratio lor frequency line, never b'ccome absolutely zero until the ratio of the unmodulated carrier to the modulated component becomes infinity. From the' curve, however, it will be S 4, the quality of the speech transmitted over the high fnequency line approaches very closely to the quahty'obtained by the lo greater than about w frequency line, and it was ,found that a ratio of 5 or 6 gives practically as good quality as a ratio S very much larger'. In tests actually made, ratios of ashigh as have been used without, however` increasing the quality appreciably more than tor a ratto of 5. For most purposes, therefore, the ratio lengths and havingdii'crent attenuation conV staats, provided the manner ot' applying cur-Y rents to the line is the same in all cases. This value. however, is useful, not onlyv in systems ot' the particular type illustrated. but since this value represents the ratio oi the carrier component to the modulated component that should bc impressed uponthe detector. the ratio thus determined may be made use of 'for proportiouiug these quantities at a receiving .station irrespective of the particular system of transmission that is used and whether the transmission system aline o1`- is a radio system.

rlhe determination ot' this ratio that is used to obtain a high degree ot' quality oi transmission is believed to be novel both as to method and to means. In view ot the va rions applications which this invention may have in the transmission and reception of signals, it is not to be construed as limited 'in any wa by the particu/lar system or ci1' cuits that lia/ve been described and il1ustrated, but itis to be limited only by the scope of the appended claims.

That is claimed is.

1 l. In signaling by higfh frequency waves, the method of controlling` the quality ot' signal reception which comprises trans-'- mittlng a signal-modulated high frequency wave, independently transmit-ting a high fre uency wave of the same frequency unmo ulated and combining;r said signal-merlulated and independently transmitted high frequency waves to produce the signal.

2. The method of signaling comprising generating a high frequency Wave, modulating a portion of said high frequency wave, transmitting said modulated wave, and independently transmitting another portion of said high frequency wave during' the whole period ot' said generation. A

3. The method of signa-ling comprisine'y modulating a high frequencywere, transA component; is substantially tive.

5. The lnetliod of determining the ratio of 'unmodulated carrier component to the .modulated component. transmitted through a high frequency telephone channei comprising measuring the strength of the vvoice cur? rents used to modulate said high frequency Wave, substituting/for the voice currents a. simple wave of equivalent energy to modulate the highfrequency wave, supplying a emitting said wave and cmnbininglvvith said il 1 litt) Cil Wave te sziid'eha-nnei :md sepemtey seieetsind measiiirig tim high ifquency cemu pement emitiie modilieteci component tained with said simple 'Wave tw'detemie tbei ratia 6. The method @t vayingr the quality of@ speech Wave' 'traiisiitted high fiequency weve compiiemg tiexismit# ting, at ali times when the-V.. ce meduiaed Wave is being. transmttedemi i?@iepen fiea'it-` .7. The metho. of tefstng the quaity olfsigneis transmitte; by iiiffh frequency waves9 when various stieiigths of tile unmoduieted cem'ponent E said high. fre-- quency Waves: me present, which eempiees currents to be tmisimitte :saliti Wevee, a

Destinia-tm' for emitroiling saif iiigfi fie.

quency waives in eccociame with :wifi sig- Daling currents ami a circuit sappig/ing, atv ali time?, when seid contoiimg action .oecu's, :a eentoiia'iie amount of 'Waves tem said semee of high frequency Wai/este said system iiidependentiy of said moduietof.

9. in a. signaiing' system, a, transmitting terminal, a, meiuietor, a source of high tref quen y Wmfega, cireuit for suppiiig Waves from saisi soufiee to said. moduiato'., e sepamt@ Qireut fer sappi ing' waves em sai; source tu seid teimina and e, baieneefi uitl cuit for preventing reaction upon said esci?- iator of currents supplied from said m0du- Wave, a transmission circuit for Con'vez'tii'ig circuit, a, fcoi'iti'eiiebie amount of sustained waves of *he said high frequency.

il. high. frequeziey telephone System conq'iiisiug a tranwiission circuit, means for supplying speeeibmeduiated high frequency warm-:s 'to said ciieut anzi eti if means' for' cmitimieusiy supplying a sust ,Led Wave 0f high fiequeney to Seid 'tiansmi5sion Cirvui et' Such magnitude that the ratio of the megas ef @Unie-orient imisautialy 1?, A eiepione Eej/@tem comprising: :1. smut mg Stationen@ et ieeeivmg station, u ifm' frequency telephone ine and. a hifghtiequeneff caljrier teiepimie'iine contesting' Said .fitntiens, means; et the ti'mifmiitt" ipj Station *for ti'mismittiiig' speenii evei beth of said inersn means tot' taisiiiii-ti`ig :i cnntrniiehie immuni mi' ui'mmduiated carrier Waves over said high equeicy iiie, and u. receiver at the eceiiing station Qpembie by speech cuirents timsmitted mei' either of Suid iines.

1li. :in a. signaiingeysftem, a. Senese et high frequency waives, f i detesto? for Waves and two paths comiectefi between said soute@ anzi said tieteet-zn, one path ineimiiiig e mociulatoi* 1d n tru-ns sesion circuit and the otiiex Mii inciuciing :in ampiier, e vmfii'abie regule li g i'evsistanee and Said tizi-nmission circuit, saifi other energy iew eendition.

'15. The method et comprising mouiating a iniggiiI frequency wave, tmnsmitting the nofuiiiteci Wave; and simuitaneousiy transmitting a wevel of Sai high frequency '0f susi). magnitne that the ratio of the iminofiuiited hiet. fi'efpiiency eemponeiit to mouiatien com ing either side band 'ie @eater than fem'.

iThe metiid et' sigmiing; cempi'ising mouiating it high frequency wave by u range nii coii-p'm'ativeiy 10W frequencies, transmitting at least one of the resuitnt side bands of frequencies, ami eimultaneois seid. hig i frequency of suffix magnitude that the totai rsizismittefi @imipenem oit.' mammie late h1 i ''iequeney wave is at ieast fioul. times :is Efe-eat as' 'the tinnsixitted. Side, bund'. if?. T e method "of sigmiiing ce; rising; mouiamngg e high fequency wey@ time mitting Saki waive imk combining with Said wave wave ef said high fieqiency of such magnimie that the ratio of the umnmii'aiateei iiigh freqt mcy component to the. imuited component le between four and six.

18. Trie meth i of Sig'nfting compiising modulating 'e high fi'equenoy 'Wa-ve, team mitting said wave, and combining with seici wave a .ive et sait?. high frequency si? Gueb. magnitude that the rat-ic of @mimi ieruieteel high 'tequency compoient to the meduiai-,tei domponent is between threesmd.

ponente )Seguiment with being' in Continuons n l). The method of signaling ('omprising lated high frequency waves to said trnnsnns` generating a high frequency waive, modulatin;r n portion of said high frequency w( ve, transmitting a single modulated side. bz nd of smid modulated ware, and independently transmitting another port-ion of` said high frequency wave during modulation;

20. A system for determining the ratio of uninodulated carrier component to the modulated Currier component which comprises, a voice frequency source, al sine Wave source forwaves of the mean' speech frequency, a high frequency source, a modulator, a transmission cnzcuit, a circut between the modulator and said transmission circuit adapted t0 transmit a Single side band of the modulated high frequency waves, means for alternateiy supplying to the modulatr Waves of equivalent enerfr from seid v01 e fre nene source n L. v l

and said sine Wave source, means lor supplying a predetermined amount of nnmodulated and the in sion circuit, and means for separately selecting and measuring the unxnoi'lulnted high frequency wave andthe modulated side band component to determine their ratio.

2l. The method of 'signaling by modulated 'waves which comprises generating and transmitting to a distant station a modulated Wave, transmitting un independei'itly controllable unmodulated wave of the carrier frequency, controlling the transmission of thennmodulate'd 1sii-ave', independently of the modulation, and operating a single reeeiver by the coo )erative action of the modupendently transmitted unmodulated wave.

In witness whereof, I hereunto subscribe my name this 27th day of September A. D.,-

' FREDERICK W. KnANZ. 

